Oscillator with electroluminescent and photoconductive elements



Aug. 27, 1963 J. MATARESE 3,102,242

OSCILLATOR WITH ELECTROLUMINESCENT AND PHOTOCONDUCTIVE ELEMENTS OriginalFiled May 1, 12. 57

! I I v 4 I r I 5 1 5 5 I I IMPEDANCE (b) 'VOLTAGE (c) VOLTAGE NW (d)T1ME- BY INVENTOR.

JOHN MATARESE A TTOR/VEX and second electrically conductive films.

United States Patent 3,102,242n OSCILLATOR WITH ELECTROLUMINESCENT ANDPHOTOCONDUCTIVE ELEMENTS John Matarese, Bronx, N.Y., assignor, by mesneassignments, to Sylvania Electric Products Inc, Wilmington, Del., acorporation of Delaware Original application May 1, 1957, Ser. No.656,338, now Patent No. 2,898,556, dated Aug. 4, 1959. Divided and thisapplication Apr. 16, 1959, Ser. No. 810,205

2 Claims. (Cl. 331-107) I My invention is directed toward electricaldevices incorporating electroluminescent and photoconductive elements.This application is a division of application Serial No. 656,338, filedMay 1, 1957, now Patent No. 2,898,556. It is an object of the presentinvention to provide a new and improved electrical device, such as anamplifier I l trical device, wherein electrical interaction betweeninput and output circuits of the device is obtained through the use oflight as a control medium.

Still another object is to provide a new and improved. electricalamplifier for oscillator incorporating electroluminescent andphotoconductive elements in parallel connection.

These and other objects of my invention will either be explained or willbecome apparent hereinafter.

In accordance with the principles of my invention, 1 provide anelectroluminescent layer, first and second opposite faces of-which arerespectively coated with first I further provide a photoconductivelayer, first and second opposite faces of which are respectively coatedwith third and fourth electrically conductive films. 'llhe first andthird films are connected to a first common terminal and constitute. a

first electrically conductive element, the second and fourth dependenceof various circuit parameters of the embodi- 3,102,242 Patented Aug. 27,1963 "ice and the voltage across the impedance element are alternatingvoltages varying at a frequency dependent upon the rate of change ofimpedance of the photoconductive layer. Hence, the arrangement disclosedabove functions as an oscillator.

If desired, the two paralleled layers can be combined with an integralstructure by placing the layers together in such manner that either thefirst and third films or the second and fourth films form a common filmin contact with one side of each layer. Provided that the common film istransparent, this structure can be connected to the series circuit inthe manner previously described and will operate in the same manner.

Illustrative embodiments of my invention will now be described in detailwith reference to the accompanying drawings wherein FIG. 1 illustratesone embodiment of my invention;

FIG. 2 illustrates another embodiment of my invention; and

FIG. 3, a, b, c and d are graphs illustrating the time ments shown inFIGS. 1 and 2.

1 'Referring now to FIG. 1, there is shown an electroluminescent layer10, opposite sides of which are coated and 20. Films 18 and 12 areconnected to a first common films are connected to a second commonterminaland constitute a second electrically conductive element.

The two layers are positioned in such manner that light emitted from theelectroluminescent layer strikes the.

photoconductive layer. The photoconductive layer must a bephotosensitive to the light emitted from the electro luminescent layer.

A series circuit including avoltage source, a switch and an impedanceelement is connected between the first and second terminals. The valueof this impedance element is much lower than the impedance representedby the across the paralleled layers and the electroluminescent layeremits light. This pulse irradiates the photoconductive layer and itsimpedance begins to decrease. As the impedance of the photoconductivelayer decreases, the voltage across the impedance element increases andthe voltage across the paralleled layers decreases. This processcontinues until the voltage across the paralleled layers is quite smalland the electroluminescent layer emits no light. The photoconductivelayer then is dark, and its impedance continuously increases toward itsoriginal value. As the impedance of the photoconductive layer increases,the voltage across the electroluminescent layer increases until theelectroluminescentlayer again emits light and the entire processrepeats.

As a result both the voltage across the paralleled layers terminal 22and constitute a first electrically conductive element; films 14 and 20are connected to a second common terminal 24 and constitute a secondelectrically conductive element. A series circuit including an impedanceelement 26, a switch 28 and a battery 30 is connected between terminals22 and 24. A light tight box 32 encloses layers 10 and 16.

The impedance of element 26 is much higher than the impedance of layer16 when illuminated and is much 7 The emitted light c'uradiates layer 16and its impedance 1 begins to decrease. As the impedance of layer 16decreases, the voltage drop across layers 10 and 16 begins to decreaseand the initially small voltage drop across element 26 begins toincrease. The light output from layer 10 which has previously attained amaximum value begins to decrease or decay.

At this point, the impedance of layer 16 begins to increase. The voltagedrop across element 26 then begins to decrease, and the voltage dropacross layers 10 and 16 begins to increase, thereby increasing theelectric field across layer 10. As the field increases, light is emittedfrom layer 10, and the process is repeated.

Consequently, alternating voltages appear across element 26 and acrossthe paralleled layers 10 and 16, the frequency, of these voltages beingdetermined primarily by the time rate of change of the impedance oflayer 16 in response to light irradiation, or stated differently, thefrequency is primarily determined by the decay period of layer 16. a

Appropriate wave forms of the variations of impedance voltages andemitted light as a function of time are shown in the drawings, whereinFIG. 3a illustrates the variation intensity of light emitted from layer10; FIG. 3b illustrates the variation in impedance of layer 16; andFIGS. 3c and 3d respectively illustrate the voltage variations acrosselement 26 and the paralleled layers 10 and 16.

FIG. 2 shows a modification of the arrangement of FIG. 1' wherein thelayers 10 and 16 are arranged one a above the other and films 14 and 20are replaced by a single transparent electrically conductive film 34 incontact with both layers. Further, the box 32 of FIG. 1 is replaced bytwo insulating light opaque films 36 and 38 which coat opposite sides ofboth layers 10 and 16. This modification functions as an oscillator inthe same manner as indicated previously.

Since the impedances of layers 10 and 16 are primarily resistive atleast to a first approximation, element 26 can take the form of aresistor and oscillations can still be produced in substantially thesame manner as above. By removing a portion of the opaque film 36 thevariations in the light emitted from layer 10 can be observed orutilized as necessary.

While I have shown and pointed out my invention as applied above, itwill be apparent to those skilled in the art that many modifications canbe made within the scope and sphere of my invention as defined in theclaims which follow.

What is claimed is:

1. An electroluminescent device comprising (a) a hollow opaque enclosurecontaining (1)) an electroluminescent layer provided with first andsecond opposite faces respectively coated with first and secondelectrically conductive films,

(c) a photoconductive layer provided with first and second facesrespectively coated with third and fourth electrically conductive filmspositioned adjacent said electroluminescent layer, saidelectroluminescent 45, layer being isolated from incident radiation bysaid opaque enclosure and said photoconductive layer receiving radiationonly from said electroluminescent layer,

(d) means electrically coupling said first and third films to a firstterminal, and

(e) means electrically coupling said second and fourth films to a secondterminal, said electroluminescent layer emitting light in response to avoltage applied across said first and second terminals when saidphotoconductive layer has a high impedance and not emitting light whensaid photoconductive layer has a low impedance, the impedance of saidphotoconductive layer being determined by the light emitted by saidelectroluminescent layer.

2. The electroluminescent device defined by claim 1 wherein the meanselectrically coupling said first and third films to said first terminalis an impedance element, said impedance element having an impedancewhich is lower than the parallel impedance of said electroluminescentand photoconductive layers when said photoconductive layer is dark andhigher than said parallel impedance when said photoconductive layer isilluminated.

References Cited in the file of this patent UNITED STATES PATENTS

1. AN ELECTROLUMINESCENT DEVICE COMPRISING (A) A HOLLOW OPAQUE ENCLOSURECONTAINING (B) AN ELECTROLUMINESCENT LAYER PROVIDED WITH FIRST ANDSECOND OPPOSITE FACES RESPECTIVELY COATED WITH FIRST AND SECONDELECTRICALLY CONDUCTIVE FILMS, (C) A PHOTOCONDUCTIVE LAYER PROVIDED WITHFIRST AND SECONDFACES RESPECTIVELY COATED WITH THIRD AND FOURTHELECTRICALLY CONDUCTIVE FILMS POSITIONED ADJACENT SAIDELCETROLUMINESCENT LAYER, SAID ELECTROLUMINESCENT LAYER BEING ISOLATEDFRM INCIDENT RADIATION BY SAID OPAQUE ENCLOSURE AND SAID PHOTOCONDUCTIVELAYER RECEIVING RADIATION ONLY FROM SAID ELECTROLYUMINESCENT LAYER,